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. 2010 Sep;1(9):941-51.
doi: 10.1177/1947601910385449.

Reduction of human embryonal rhabdomyosarcoma tumor growth by inhibition of the hedgehog signaling pathway

Affiliations

Reduction of human embryonal rhabdomyosarcoma tumor growth by inhibition of the hedgehog signaling pathway

Ulrica Tostar et al. Genes Cancer. 2010 Sep.

Abstract

Rhabdomyosarcoma (RMS) is the most frequent soft-tissue sarcoma in children. Embryonal rhabdomyosarcoma (E-RMS) represents the most common RMS subtype, but the molecular events driving this tumor are still largely unknown. The hedgehog (HH) pathway, a major signal transduction cascade, is linked with many cancers, including RMS. As we previously have detected loss of heterozygosity of PTCH1 in E-RMS, we now examined 8 E-RMS tumor samples and 5 E-RMS cell lines for the presence of PTCH1 mutations, but none was detected. However, in the E-RMS cell lines, a variable pattern of up-regulated expression of certain HH signaling target genes, including HHIP, PTCH1, SFRP1, and GLI1, was observed. Moreover, treatment with the small molecule HH signaling inhibitors cyclopamine and GANT61 inhibited cell proliferation in all E-RMS cell lines analyzed. Interestingly, GANT61 was more effective, and this was accompanied by increased apoptosis, while cyclopamine promoted necrotic events. Specific knockdown of SMO had no effect on the proliferation of E-RMS cells, indicating the presence of an SMO-independent HH signaling pathway in the E-RMS cell lines. Furthermore, in an in vivo xenograft model, tumor growth was significantly reduced by GANT61 treatment of E-RMS cells. Additionally, siRNA experiments provided evidence that inhibition of GLI1 or GLI3 but not GLI2 was sufficient to reduce proliferation of these cell lines. As GANT61 is known to block GLI1/GLI2 transcriptional activity, the inhibition of E-RMS growth by GANT61 is likely to be mediated through GLI1. In conclusion, our findings implicate that GLI1 could constitute an effective therapeutic target in pediatric E-RMS.

Keywords: GANT; GLI; embryonal rhabdomyosarcoma; hedgehog signaling.

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Conflict of interest statement

The author(s) declared no potential conflicts of interest with respect to the authorship and/or publication of this article.

Figures

Figure 1.
Figure 1.
E-RMS cells express HH signaling target genes and components of the pathway. (A) Real-time RT-PCR analysis of the HH pathway target genes PTCH1, HHIP, and SFRP1 expression in the E-RMS cell lines JR-1, RD, Rh36, CCA, and CT-TC and the EWS cell line A673. (B) Real-time RT-PCR analysis of GLI1, GLI2, GLI3, and SMO expression in the E-RMS cell lines and the EWS cell line. For both (A and B), the expression levels relative to human fetal skeletal muscle cells (HFSMC), after normalization for the housekeeping gene GAPDH, are shown.
Figure 2.
Figure 2.
E-RMS cells are sensitive to treatment with HH signaling inhibitors. (A) Phase contrast micrographs depicting the morphology of the JR-1, RD, Rh36, CCA, and CT-TC E-RMS and the A673 EWS cell lines following HH signaling inhibition. The cells were treated with 10 µM concentrations of the inhibitors for 7 days and compared with the DMSO control. Scale bars, 100 µm. Note that cyclopamine and GANT61 inhibit at variable degrees the growth of E-RMS but not EWS cells. (B) Cyclopamine or GANT61 treatment for 72 hours inhibits the proliferation of the E-RMS but not the EWS cells. Proliferation was assayed by EdU incorporation for 2 hours. The percentage of cells labeled with Alexa fluor 488 azide and detected by flow cytometry is shown.
Figure 3.
Figure 3.
The HH signaling inhibitor GANT61 has an impact on HH target gene expression and reduces proliferation of E-RMS cells through apoptotic mechanisms, while SMO is dispensable for cellular growth. (A) Real-time RT-PCR analysis of the expression of the HH pathway target genes HHIP and GLI1 following HH signaling inhibition. A673, CCA, and Rh36 cells were treated for 24 hours with 10 µM concentrations of cyclopamine or GANT61. Shown are the mRNA levels relative to the DMSO control normalized to the mean expression of the housekeeping genes TBP and GAPDH. (B) GANT61 treatment significantly increases apoptosis in CCA and Rh36 cells. Shown are the apoptotic (annexin V–positive and PI-negative) cells within the green square and the necrotic (PI-positive) cells within the blue square, analyzed by flow cytometry. The percentage of total cells in the green and blue squares is indicated. (C) Real-time RT-PCR analysis of the SMO expression levels in CCA and Rh36 cells 48 hours after transfection with siRNAs directed against SMO (siSMO) or a nontargeting control (siNT). The mRNA levels are normalized to the mean expression of the housekeeping genes TBP and GAPDH. (D) Proliferation of CCA and Rh36 cells is unaffected by siSMO treatment. Cells were cultured for 72 hours after siRNA transfection followed by EdU incorporation for 3 hours. The percentage of cells labeled with Alexa fluor 488 azide and detected by flow cytometry is shown.
Figure 4.
Figure 4.
GANT61 reduces growth of E-RMS in vivo. (A) Five × 106 cells from the CCA, Rh36, or A673 cell lines were mixed with DMSO or 10 µM or 30 µM GANT61, introduced into chick CAMs, and allowed to grow for 7 days. After resection and trimming, tumors were photographed, with representative ones from each group shown. Scale bar, 1 cm. The CAM experiments were repeated 3 times with similar outcomes. (B) Tumor weights are represented as scatter plots, with the lines denoting mean ± standard deviation. The decrease in tumor weight of 30 µM GANT61-treated relative to DMSO-treated Rh36 cells reached statistical significance (P = 0.0173), indicated in the plot by an asterisk. (C) Immunohistochemical staining of the tumors for Ki67 (brown precipitate) revealed a comparable degree of proliferation despite the different sizes of the tumor mass. The unstained region surrounding the tumors is the CAM tissue (arrowhead).
Figure 5.
Figure 5.
Role of GLI1, GLI2, and GLI3 for the proliferation of E-RMS cells. (A) Western blot analysis of extracts from A673, CCA, and Rh36 cells. The full-length (FL) 190-kD activator and the repressor (R) 83-kD GLI3 forms are indicated. αβ-tubulin was used as a loading control. (B) Real-time RT-PCR analysis of the GLI1, GLI2, and GLI3 expression levels in CCA and Rh36 cells 48 hours after transfection with siRNAs directed against GLI1 (siGLI1), GLI2 (siGLI2), GLI3 (siGLI3), or a nontargeting control (siNT). The mRNA levels are normalized to the mean expression of the housekeeping genes TBP and GAPDH. (C) Proliferation of CCA and Rh36 cells is reduced by siGLI1 or siGLI3 but not siGLI2 treatment. Cells were cultured for 72 hours after siRNA transfection followed by EdU incorporation for 2 hours. The percentage of cells labeled with Alexa fluor 488 azide and detected by flow cytometry is shown.

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